In a semiconductor manufacturing apparatus, a semiconductor wafer (hereinafter, referred to as “wafer”) that is a circular substrate is transferred to a processing module by a transfer unit and subjected to processing. Before the wafer is transferred to the processing module by the transfer unit, the wafer may be transferred to an alignment apparatus so that a direction and a position of a circumferential edge thereof can be detected. The transfer unit receives the wafer from the alignment apparatus, and transfers the wafer to a predetermined location in the processing module to be directed in a predetermined orientation based on the detection result.
Conventionally, a wafer has a cutoff portion referred to as a notch that indicates a orientation thereof. The alignment apparatus has a transmission-type sensor so that a orientation of the notch and a location of the circumferential edge of the wafer can be detected. However, a recent wafer having a diameter of 450 mm may have a fiducial mark (hereinafter, referred to as “alignment mark”) that is a dot-shaped laser mark, instead of the notch, near a circumferential edge of a backside thereof. Accordingly, the alignment apparatus has a camera that is a reflective type sensor, and the alignment mark and the circumferential edge of the wafer are detected by imaging the wafer by the camera while a light source irradiates the wafer with light.
An slanted surface referred to as a beveled portion is formed at a top surface and a backside of a peripheral end portion of the wafer. As will be described in detail in “Detailed Description of the Embodiments”, due to the beveled portion of the above shape, the reflection state of the light from the light source becomes different between the beveled portion of the wafer and a portion of the wafer located at an inner side than the beveled portion, which makes it difficult to accurately detect the circumferential edge of the wafer. Japanese Patent Application Publication No. 2009-88184 discloses a technique for obtaining an image including a contour of a wafer by a camera and obtaining a position of the wafer based on the image. However, there are not disclosed the above drawback and a solution.